Machine dishwashing detergents constitute a generally recognized distinct class of detergent compositions, particularly as compared to detergents designed for fabric laundering. As an example, a spotless and film-free appearance of glasses and silverware is the expected final result of a machine dishwashing run while, in many laundering operations, substances which may leave a greasy, oily or soapy residue can be tolerated.
In general, machine dishwashing detergents are mixtures of ingredients whose purpose, in combination, is to break down and remove food soils; to inhibit foaming caused by certain food soils; and to remove stains such as might be caused by beverages such as coffee and tea or by vegetable soils such as carotenoid soils. While necessary for these various cleaning benefits, machine dishwashing detergents can also create or exacerbate other problems. As an example, carbonate and phosphate salts, often detergent ingredients, are known to contribute to the formation of hard water films on glasses. In European applications, the water used to prepare the solution for the washing process is often treated (softened) to remove hardness ions such as calcium and magnesium with the result that hard water residues on washware are reduced. Nevertheless, spotting and filming from soil residues and precipitates from the detergent formulation can remain a problem, especially if the ion exchange unit serving the dishwashing machine is operating inefficiently.
Conventional machine dishwashing detergents employ strong alkalis such as sodium hydroxide, bleaches such as hypochlorite, and builders such as phosphates in order to assist in the cleaning steps outlined above. However, environmental factors, such as restrictions on phosphate and chlorine levels, and safety considerations have lead to the search for a new class of lower pH detergent formulations. Further, conventional formulations can damage items unique to machine dishwashing such as silverware, glassware and dishware. Certain of these items can be expensive to replace and force the consumer to separate them out from the rest of the table ware for hand washing--an obvious inconvenience. This new class of detergent formulations employs various detersive enzymes, including amylolytic and proteolytic enzymes, to compensate for the loss in cleaning effectiveness inherent at these lower pH values. Unfortunately, the conventional hypochlorite bleach system is incompatible with this enzymatic route and, as a consequence, oxygen bleaching systems have been adopted.
While the soil removal properties of these enzymatic formulations can match that of the conventional detergents, they have one notable weakness in the area of spotting and filming on glasses. The absence of chlorine bleach, alkalinity and phosphate builders generally results in higher spotting and filming scores under controlled laboratory testing and in a higher frequency of complaints from consumers in these two areas.
Spotting and filming of glassware are the chief criteria by which the performance of a dishwashing formulation is judged. Spotting is an obvious reference to discrete residues on glassware which have resulted when water droplets have completely evaporated and left behind any dissolved solids. Filming refers to a more uniform deposition over a large, contiguous portion of the glass surface. Without wishing to be bound by theory, it is believed that this film can sometimes be of organic origin (resulting from soil in the wash liquor) but is also often inorganic in nature, due to the formation of some mineral precipitate.
Accordingly, it is an object of the present invention to provide a new and improved machine dishwashing composition. Preferred compositions are free from chlorine bleach but may, optionally, contain an oxygen bleach. It is another object herein to provide dishwashing detergent compositions which contain effective levels of a cationic or amphoteric polymer which provides superior glassware appearance as evidenced by reduced spotting and filming. Another object herein is to provide a dishwashing rinse aid formulation containing an effective level of the cationic or amphoteric polymer.